It is proposed to study autoantibodies in rheumatoid arthritis. Particular attention will be given to IgG rheumatoid factor. IgG rheumatoid factor complexes will be isolated from the serum of patients with Felty's syndrome and rheumatoid vasculitis and from the synovial fluid of patients with rheumatoid arthritis. These will be compared in regard to sedimentation coefficients, complement activation and binding to Clq and monoclonal IgM rheumatoid factor. This will be done in order to investigate possible differences in these apparently similar immune complexes insofar as they appear to be responsible for varying immunopathological activities.